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Abstract:

An inkjet printer contains an aqueous inkjet ink exhibiting good jetting
reliability and ink storage stability, comprising:
a) water;
b) colored pigment exhibiting a median volume weighted 50th
percentile particle size of less than 0.11 microns;
c) from 0.1% to 4% by weight of a compound I represented by the following
Structure (I):
##STR00001##
d) and a polyurethane latex binder.

Claims:

1. An inkjet printer containing an aqueous inkjet ink, comprising:a) at
least 50% by weight water;b) from 0.1% to 3% by weight, in toto, of
dispersed colored pigment exhibiting a median volume weighted 50.sup.th
percentile particle size of less than 0.11 microns;c) from 0.1% to 4% by
weight of a compound I represented by the following Structure (I):
##STR00004## wherein R4 is chosen from the group consisting of --H,
--CH3, --C2H5, --C3H7, and
--CH2O(CH2CHR5O).sub.x4H;1) provided when R4 is --H,
--CH3, --C2H5, or --C3H7, each of R1,
R2 and R3 are independently hydrogen or methyl, b is 0 or 1;
x1, x2 and x3 are each equal to at least 1, and the sum of
x1, x2 and x3 is 3 to 21, and2) provided when R4 is
--CH2O(CH2CHR5O).sub.x4H, each of R1, R2,
R3 and R5 is independently hydrogen or methyl; b is 0 or 1 and
the sum x1, x2, x3, and x4 is from 3 to 28;d) from
0.05% to 3% by weight of a polyurethane latex binder;e) optionally, a
water soluble polyacrylate polymer in an amount less than 3% by weight;f)
provided that the sum of the polyurethane latex binder and any water
soluble polyacrylate polymer is not more than 3% by weight; andg) further
provided that the weight ratio of dispersed pigment to the sum of all
water soluble polyacrylate polymer and polyurethane latex binder is from
3:1 to 1:2.

2. The inkjet printer of claim 1 wherein the ink comprises a water soluble
polyacrylate polymer in an amount less than 3% by weight.

3. The inkjet printer of claim 1 wherein said dispersed pigment is a
surfactant dispersed, self-dispersed, or encapsulating-dispersant
dispersed pigment.

4. The inkjet printer of claim 3 wherein said dispersed pigment is
surfactant dispersed and the surfactant is a metal salt of
oleylmethyltaurate.

5. The inkjet printer of claim 1 wherein said dispersed colored pigment is
chosen from the group consisting of cyan, magenta, yellow, red, green,
blue, violet, and orange colored pigments.

6. The inkjet printer of claim 1 wherein said dispersed pigment is a black
colored pigment.

7. The inkjet printer of claim 1 wherein R4 is
--CH2O(CH2CHR5O).sub.x4H and R5 is hydrogen or
methyl.

8. The inkjet printer of claim 1 wherein the compound of structure I is
present at from 1% to 3% by weight.

9. The inkjet printer of claim 1 wherein the water soluble polyacrylate
polymer exhibits an acid number from 100 to 400 and a weight average
molecular weight Mw from 5,000 to 20,000.

10. The inkjet printer of claim 1 wherein polyurethane latex binder
exhibits an acid number from 60 to 150 and a weight average molecular
weight between Mw from 7,500 to 30,000.

11. The inkjet printer of claim 1 that is free of an ejection disabling
quantity, less than 0.05 wt. %, of a water soluble amine.

12. An inkjet ink set comprising at least two distinctly colored inks, at
least one comprising:a) at least 50% by weight water;b) from 0.1% to 3%
by weight, in toto, of dispersed colored pigment exhibiting a median
volume weighted 50.sup.th percentile particle size of less than 0.11
microns;c) from 0.1% to 4% by weight of a compound I represented by the
following Structure (I): ##STR00005## wherein R4 is chosen from the
group consisting of --H, --CH3, --C2H5, --C3H7,
and --CH2O(CH2CHR5O).sub.x4H;1) provided when R4 is
--H, --CH3, --C2H5, or --C3H7, each of R1,
R2 and R3 are independently hydrogen or methyl, b is 0 or 1;
x1, x2 and x3 are each equal to at least 1, and the sum of
x1, x2 and x3 is 3 to 21, and2) provided when R4 is
--CH2O(CH2CHR5O).sub.x4H, each of R1, R2 R3
and R5 is independently hydrogen or methyl; b is 0 or 1 and the sum
x1, x2, x3, and x4 is from 3 to 28;d) from 0.05% to
3% by weight of a polyurethane latex binder;e) optionally, a water
soluble polyacrylate polymer in an amount less than 3% by weight;f)
provided that the sum of the polyurethane latex binder and any water
soluble polyacrylate polymer is not more than 3% by weight; andg) further
provided that the weight ratio of dispersed pigment to the sum of all
water soluble polyacrylate polymer and polyurethane latex binder is from
3:1 to 1:2.

13. An inkjet ink set comprising at least two commonly colored inks, at
least two inks with the prescribed limitations of claim 12.

14. An inkjet recording method comprising the step of applying to a
receiving element an ink, comprising:a) at least 50% by weight water;b)
from 0.1% to 3% by weight, in toto, of dispersed colored pigment
exhibiting a median volume weighted 50.sup.th percentile particle size of
less than 0.11 microns;c) from 0.1% to 4% by weight of a compound I
represented by the following Structure (I): ##STR00006## wherein R4
is chosen from the group consisting of --H, --CH3, --C2H5,
--C3H7, and --CH2O(CH2CHR5O).sub.x4H;1) provided
when R4 is --H, --CH3, --C2H5, or --C3H7,
each of R1, R2 and R3 are independently hydrogen or
methyl, b is 0 or 1; x1, x2, and x3 are each equal to at
least 1, and the sum of x1, x2 and x3 is 3 to 21, and2)
provided when R4 is --CH2O(CH2CHR5O).sub.x4H, each of
R1, R2, R3, and R5 is independently hydrogen or
methyl; b is 0 or 1 and the sum x1, x2, x3, and x4 is
from 3 to 28;d) from 0.05% to 3% by weight of a polyurethane latex
binder;e) optionally, a water soluble polyacrylate polymer in an amount
less than 3% by weight;f) provided that the sum of the polyurethane latex
binder and any water soluble polyacrylate polymer is not more than 3% by
weight; andg) further provided that the weight ratio of dispersed pigment
to the sum of all water soluble polyacrylate polymer and polyurethane
latex binder is from 3:1 to 1:2.

15. An inkjet recording method according to claim 14, using a printer with
a thermal or piezo ejection head, to jet at least two distinct inks, each
according to claim 14.

Description:

FIELD OF THE INVENTION

[0001]The invention relates to inkjet printers containing inkjet inks
comprising fine-grained pigment particles, polyoxygenated polyols and a
polyurethane latex polymer as well as inkjet inkjets comprising such
inks, the inks themselves, and methods of applying such inks to media.

BACKGROUND OF THE INVENTION

[0002]Inkjet printing is a non-impact method for producing printed images
by the deposition of ink droplets in a pixel-by-pixel manner to an
image-recording element in response to digital data signals. There are
various methods that can be utilized to control the deposition of ink
droplets on the image-recording element to yield the desired printed
image. In one process, known as drop-on-demand inkjet, individual ink
droplets are projected as needed onto the image-recording element to form
the desired printed image. Common methods of controlling the projection
of ink droplets in drop-on-demand printing include piezoelectric
transducers and thermal bubble formation. In another process, known as
continuous inkjet, a continuous stream of droplets is charged and
deflected in an image-wise manner onto the surface of the image-recording
element, while un-imaged droplets are caught and returned to an ink sump.
Inkjet printers have found broad applications across markets ranging from
desktop document and photographic-quality imaging, to short run printing
and industrial labeling.

[0003]Early inkjet inks were formulated much like conventional printing or
pen-applied inks. As greater attention has been directed towards printing
speed, ease of use, reliability, and environmental issues and with
increasing interest in forming improved images, inks have been formulated
to work well on specific media. For example, inks intended to provide
durable and glossy images on photo-glossy image receivers can incorporate
film forming polymers and soluble dye colorants while inks intended to
provide well adhering fast drying, smooth images on plain papers can
include soluble dye colorants, paper penetrants and paper anti-curl
agents. The soluble dye inks all suffer from light fade, a problem that
is especially significant when archival photo-images are desired and from
poor resistance to rewetting. It has been proposed to alleviate the light
fade problem by providing dispersed pigment as colorants in place of
soluble dyes. However, use of pigments often leads to a reduction in
image gloss and poor rub resistance on coated media such as photo-glossy
media and image inhomogeneity or mottle on plain papers and related
untreated media. Jetting has been improved by the use of polymers
intended to act as jetting aids.

[0004]However, jetting reliability and ink storage stability remains an
issue especially with pigmented inks when a low-density forming or light
ink is desired as in the preparation and use of the so-called photo-inks
and in proofing inks.

SUMMARY OF THE INVENTION

[0005]An inkjet printer containing an aqueous inkjet ink, comprising:

[0006]a) at least 50% by weight water;

[0007]b) from 0.1% to 3% by weight of dispersed colored pigment exhibiting
a median volume weighted 50th percentile particle size of less than
0.11 microns;

[0008]c) from 0.1% to 4% by weight of a compound I represented by the
following Structure (I):

##STR00002##

wherein R4 is chosen from the group consisting of --H, --CH3,
--C2H5, --C3H7, and
--CH2O(CH2CHR5O).sub.x4H; [0009]1) provided when R4
is --H, --CH3, --C2H5, or --C3H7, each of
R1, R2, and R3 are independently hydrogen or methyl, b is
0 or 1; x1, x2 and x3 are each equal to at least 1, and
the sum of x1, x2, and x3 is 3 to 21; and [0010]2)
provided when R4 is --CH2O(CH2CHR5O).sub.x4H, each of
R1, R2, R3, and R5 is independently hydrogen or
methyl; b is 0 or 1 and the sum x1, x2, x3, and x4 is
from 3 to 28;

[0011]d) a polyurethane latex binder in an amount from 0.05% to 3% by
weight;

[0012]e) optionally, a water soluble polyacrylate polymer in an amount
less than 3% by weight;

[0013]f) provided that the sum of the polyurethane latex binder and any
water soluble polyacrylate polymer is not more than 3% by weight; and

[0014]g) further provided that the weight ratio of dispersed pigment to
the sum of all water soluble polyacrylate polymer and polyurethane latex
binder is from 3:1 to 1:2.

[0015]The invention also provides an inkjet set, the inks themselves, and
a method for printing using an inkjet printer. The printer, ink set, ink,
and method of the invention provide improved jetting reliability and ink
storage.

BRIEF DESCRIPTION OF THE DRAWING

[0016]The FIGURE is a schematic view of an inkjet printer useful in the
invention.

DETAILED DESCRIPTION OF THE INVENTION

[0017]The invention is summarized above. Inkjet printing systems useful in
the invention comprise a printer, at least one ink, and an image
recording element, typically a sheet, (herein also "media"), suitable for
receiving ink from an inkjet printer. The method of the invention employs
the inkjet printer of the invention to provide an image on media. Inkjet
printing is a non-impact method for producing printed images by the
deposition of ink droplets in a pixel-by-pixel manner to an
image-recording element in response to digital data signals. There are
various methods that may be utilized to control the deposition of ink
droplets on the image-recording element to yield the desired printed
image. In one process, known as drop-on-demand inkjet, individual ink
droplets are projected as needed onto the image-recording element to form
the desired printed image. Common methods of controlling the projection
of ink droplets in drop-on-demand printing include piezoelectric
transducers, thermal bubble formation or an actuator that is made to
move.

[0018]Drop-On-Demand (DOD) liquid emission devices have been known as ink
printing devices in inkjet printing systems for many years. Early devices
were based on piezoelectric actuators such as are disclosed by Kyser et
al. in U.S. Pat. No. 3,946,398; and Stemme in U.S. Pat. No. 3,747,120. A
currently popular form of inkjet printing, thermal inkjet (or "thermal
bubble jet"), uses electrically resistive heaters to generate vapor
bubbles which cause drop emission, as is discussed by Hara et al. in U.S.
Pat. No. 4,296,421. In another process, known as continuous inkjet, a
continuous stream of droplets is generated, a portion of which are
deflected in an image-wise manner onto the surface of the image-recording
element, while un-imaged droplets are caught and returned to an ink sump.
Continuous inkjet printers are disclosed in U.S. Pat. Nos. 6,588,888;
6,554,410; 6,682,182; 6,793,328; 6,866,370; 6,575,566; and 6,517,197.

[0019]The FIGURE shows one schematic example of an inkjet printer 10 that
includes a protective cover 40 for the internal components of the
printer. The printer contains a recording media supply 20 in a tray. The
printer includes one or more ink tanks 18 (shown here as having four
inks) that supply ink to a printhead 30. The printhead 30 and ink tanks
18 are mounted on a carriage 100. The printer includes a source of image
data 12 that provides signals that are interpreted by a controller (not
shown) as being commands to eject drops of ink from the printhead 30.
Printheads may be integral with the ink tanks or separate. Exemplary
printheads are described in U.S. Pat. No. 7,350,902. In a typical
printing operation a media sheet travels from the recording media supply
20 in a media supply tray to a region where the printhead 30 deposits
droplets of ink onto the media sheet. The printed media collection 22 is
accumulated in an output tray. In another specifically contemplated
embodiment, the printable media is supplied in roll form and printed
output is detached after printing. Any known printable media can be
employed.

[0020]Suitably, the dispersed pigment useful in the invention is chosen
from the group consisting of a surfactant dispersed, self-dispersed or
encapsulating-dispersant dispersed pigment. In one embodiment, the
dispersed pigment is a surfactant dispersed pigment. When the dispersed
pigment is a surfactant dispersed pigment, the dispersing surfactant is
preferably a metal salt of oleylmethyltaurate. While any suitable metal
salt can be employed, sodium or potassium cations are most preferred. The
dispersed colored pigment can be of any suitable color but is preferably
chosen from the group consisting of cyan, magenta, yellow, red, green,
blue, violet, orange, and black colored pigments. While any Compound I
according to the structure can be employed, in one mode the compound
comprises four hydroxyl groups. In another mode, R4 is
--CH2O(CH2CHR5O).sub.x4H and R5 is hydrogen or
methyl. In a further mode, the compound of structure I is present from 1%
to 3% by weight. In another embodiment, Compound I according to the
structure comprises three hydroxyl groups and three polyoxyethylene or
polyoxypropylene branches. The water soluble polyacrylate polymer
preferably exhibits an acid number from 100 to 400 and a weight average
molecular weight Mw from 5,000 to 20,000. The polyurethane latex binder
preferably exhibits an acid number from 60 to 150 and a weight average
molecular weight Mw from 7,500 to 30,000.

[0021]The benefits of the invention are further provided by an inkjet ink
set comprising at least two distinctly colored inks, both according to
the formulation described above. In yet another embodiment, the benefits
of the invention are provided by an inkjet ink set comprising at least
two commonly colored inks, at least one of which is an ink according to
the formulation described above. In yet another embodiment, the benefits
of the invention are provided by an inkjet recording method comprising
the step of applying to a paper by thermal or piezo ejection an ink
according to the formulation described above.

[0022]While ink compositions known in the art of inkjet printing can be
aqueous- or solvent-based, and in a liquid, solid or gel state at room
temperature and pressure. Aqueous-based ink compositions are preferred in
the present invention because they are more environmentally friendly as
compared to solvent-based inks, plus most printheads are designed for use
with aqueous-based inks. By aqueous inks is meant that the ink
composition comprises at least 50% and, suitably, at least 65% by weight
water.

[0023]The ink composition can be colored with pigments, dyes, polymeric
dyes, loaded-dye/latex particles, or any other types of colorants, or
combinations thereof. Pigment-based ink compositions are preferred in the
invention because such inks render printed images having higher optical
densities, and better fade resistance to light and ozone exposure as
compared to printed images made from other types of colorants. The ink
composition can be yellow, magenta, cyan, black, gray, red, violet, blue,
green, orange, brown, etc. The ink is colored by the dispersed pigment
colorant. The inks of the invention can have one pigment colorant or
mixtures of more that one pigment colorant.

[0024]The dispersed colored pigments are present in toto at from 0.1% to
3% by weight in the inks. In one mode, the dispersed colored pigments are
present at from 0.2% to 2% by weight and in a convenient mode are present
at from 0.4% to 1.1% by weight. When mixtures of pigments are employed,
the individual dispersed colored pigments are present typically at from
0.05% to 2% by weight. The dispersed pigment colorant exhibits a median
volume weighted 50th percentile particle size of less than 0.11
microns. The ink desirably has dispersed pigment colorant particles
exhibiting a median volume weighted 50th percentile particle size of
from 0.001 to 0.09 microns. Suitably, the ink has dispersed pigment
colorant particles exhibiting a median volume weighted 50th
percentile particle size of from 0.008 to 0.08 microns. Smaller pigment
particles may form less stable images, while larger pigment particles may
fail to provide adequate gloss characteristics on some printing media.

[0025]A wide variety of organic and inorganic pigments, alone or in
combination with additional pigments or dyes can be used in the ink
composition of the present invention. Pigments that can be used in the
invention include those disclosed in, for example, U.S. Pat. Nos.
5,026,427; 5,086,698; 5,141,556; 5,160,370; and 5,169,436. The exact
choice of pigments will depend upon the specific application and
performance requirements such as color reproduction and image stability.

[0028]The preferred pigment-based ink compositions employing surfactant
dispersed pigments that are useful in the invention can be prepared by
any known method. Useful methods commonly involve two steps: (a) a
dispersing or milling step to break up the pigments to primary particles,
where primary particle is defined as the smallest identifiable
subdivision in a particulate system, and (b) a dilution step in which the
pigment dispersion from step (a) is diluted with the remaining ink
components to give a working strength ink.

[0029]The milling step (a) is carried out using any type of grinding mill
such as a media mill, a ball mill, a two-roll mill, a three-roll mill, a
bead mill, and air-jet mill, an attritor, or a liquid interaction
chamber. In the milling step (a), pigments are optionally suspended in a
medium that is typically the same as or similar to the medium used to
dilute the pigment dispersion in step (b). Inert milling media are
optionally present in the milling step (a) in order to facilitate break
up of the pigments to primary particles. Inert milling media include such
materials as polymeric beads, glasses, ceramics, metals and plastics as
described, for example, in U.S. Pat. No. 5,891,231. Milling media are
removed from either the pigment dispersion obtained in step (a) or from
the ink composition obtained in step (b).

[0030]A dispersant is optionally present in the milling step (a) in order
to facilitate break up of the pigments into primary particles. For the
pigment dispersion obtained in step (a) or the ink composition obtained
in step (b), a dispersant is optionally present in order to maintain
particle stability and prevent settling. Dispersants suitable for use in
the invention include, but are not limited to, those commonly used in the
art of inkjet printing. For aqueous pigment-based ink compositions,
particularly useful dispersants include anionic, cationic or nonionic
surfactants such as sodium dodecylsulfate, or potassium or sodium
oleylmethyltaurate as described in, for example, U.S. Pat. Nos.
5,679,138; 5,651,813; or 5,985,017.

[0031]Self-dispersing pigments that are dispersible without the use of a
dispersant or surfactant can be used in the invention. Pigments of this
type are those that have been subjected to a surface treatment such as
oxidation/reduction, acid/base treatment, or functionalization through
coupling chemistry. The surface treatment can render the surface of the
pigment with anionic, cationic or non-ionic groups such that a separate
dispersant is not necessary. The preparation and use of covalently
functionalized self-dispersed pigments suitable for inkjet printing are
reported by Bergemann et al. in U.S. Pat. Nos. 6,758,891 and 6,660,075;
Belmont in U.S. Pat. No. 5,554,739; Adams and Belmont in U.S. Pat. No.
5,707,432; Johnson and Belmont in U.S. Pat. Nos. 5,803,959 and 5,922,118;
Johnson et al. in U.S. Pat. No. 5,837,045; Yu et al. in U.S. Pat. No.
6,494,943; and in WO/PCT Published Applications: WO 96/18695, WO
96/18696, WO 96/18689, WO 99/51690, WO 00/05313, and WO 01/51566; Osumi
et al. in U.S. Pat. Nos. 6,280,513 and 6,506,239; Karl et al. in U.S.
Pat. No. 6,503,311; Yeh et al. in U.S. Pat. No. 6,852,156; Ito et al. in
U.S. Pat. No. 6,488,753; and Momose et al. in European Patent No.
1,479,732 A1. Examples of commercially available self-dispersing type
pigments include Cab-O-Jet 200®, Cab-O-Jet-250®,
Cab-O-Jet-260®, Cab-O-Jet-270®, and Cab-O-Jet 300® (Cabot
Specialty Chemicals, Inc.); and Bonjet CW-1® and CW-2® (Orient
Chemical Industries, Ltd.).

[0032]Encapsulating type polymeric dispersants and polymeric dispersed
pigments thereof can also be used in the invention. Specific examples are
described in U.S. Pat. Nos. 6,723,785 and 6,852,777; U.S. Publication
Numbers: 2004/0132942; 2005/0020731; 2005/00951; 2005/0075416;
2005/0124726; 2004/007749; and 2005/0124728. Encapsulating type polymeric
dispersants can be especially useful because of their high dispersion
stability on keeping and low degree of interaction with ink components.

[0033]Composite colorant particles having a colorant phase and a polymer
phase are also useful in aqueous pigment-based inks of the invention.
Composite colorant particles are formed by polymerizing monomers in the
presence of pigments; see for example, U.S. patent application Ser. Nos.
10/446,013; 10/446,059; or 10/665,960. Microencapsulated-type pigment
particles are also useful and consist of pigment particles coated with a
resin film; see for example U.S. Pat. No. 6,074,467.

[0035]Also useful in the invention are polymeric dyes or loaded-dye/latex
particles. Examples of polymeric dyes are described in U.S. Pat. No.
6,457,822 and references therein. Examples of loaded-dye/latex particles
are described in U.S. Pat. No. 6,431,700 and U.S. patent application Ser.
Nos. 10/393,235; 10/393,061; 10/264,740; 10/020,694; and 10/017,729.

[0036]The supplemental colorants used in the ink composition of the
invention can be present in any effective amount, generally from 0.1% to
10% by weight, and preferably from 0.5% to 6% by weight.

[0037]The inkjet inks of the invention include from 0.1% to 4% by weight
of Compound I represented by the following Structure (I):

##STR00003##

[0038]wherein R4 is chosen from the group consisting of --H,
--CH3, --C2H5, --C3H7, and
--CH2O(CH2CHR5O).sub.x4H; when R4 is --H, --CH3,
--C2H5, or --C3H7, each of R1, R2 and
R3 are independently hydrogen or methyl, b is 0 or 1; x1,
x2 and X3 are each equal to at least 1, and the sum of x1,
x2 and x3 is 3 to 21, and when R4 is
--CH2O(CH2CHR5O).sub.x4H, each of R1, R2,
R3 and R5 is independently hydrogen or methyl; b is 0 or 1 and
the sum x1, x2, x3, and x4 is from 3 to 28; In one
mode, Compound I comprises four hydroxyl groups. In another mode, R4
is --CH2O(CH2CHR5O).sub.x4H and R5 is hydrogen or
methyl. In a suitable ink, Compound I is present at from 1 to 3% by
weight. In another embodiment, Compound I according to the structure
comprises three hydroxyl groups and three polyoxyethylene or
polyoxypropylene moiety containing branches. In any event, Compound I can
have either polyoxyethylene or polyoxypropylene moiety containing
branches or mixtures of both polyoxyethylene and polyoxypropylene moiety
containing branches.

[0039]Specific embodiments of compounds according to Structure I include,
but are not limited to, the glycerol ethoxides, glycerol propoxides,
glyceryths, pentaerythritol ethoxides, and pentaerythritol propoxides.

[0040]Inks of the invention comprise from 0.05% to 3% by weight of a water
soluble polyurethane latex binder. The polyurethane latex binder is
conveniently present at from 0.1% to 2% by weight, and desirably present
at from 0.2% to 1% by weight.

[0041]The polyurethane latex binder is formed from at least one monomer
comprising at least two hydroxyl groups and at least one carboxyl group
and another monomer comprising at least two isocyanate groups. While
diisocyanates are typically used in the art of polyurethane chemistry,
triisocyanates can also be used. Examples of diisocyanates include
isophorone diisocyanate, hexamethylene diisocyanate, toluene
diisocyanate, tetramethylene diisocyanate, diphenylmethylene
diisocyanate, and other diisocyanates as known in the polymer arts. The
polyurethanes used in the invention are optionally derived from an
additional monomer comprising at least two hydroxyl groups and which is
different from the monomer having at least two hydroxyl groups. These
optional monomers are typically higher molecular weight monomers having a
molecular weight of less than 3000. They are often referred to in the art
as polyols. Examples include polyols and polyhydroxy derivatives of
polycarbonates, polyethers, polyesters, polyacetals, polyacrylates,
polyester amides and polythioethers. Preferably the optional monomer is a
polycarbonate. More preferably, the optional monomer comprising at least
two hydroxyl groups is a poly (hexamethylene carbonate) diol. Examples of
monomers comprising at least two hydroxyl groups and at least one
carboxylic acid group are 2,2-bis(hydroxymethyl)propionic acid and the
hydroxyethylether of 4,4-bis (4-hydroxyphenyl)-valeric acid. Other
examples are described in U.S. Pat. No. 6,268,101 and U.S. Publication
No. 2003/0184629 and references cited therein. Water-dispersible
polyurethanes are disclosed as binders in pigmented inks in U.S. Pat. No.
6,533,408, and particularly useful polyurethanes for pigmented inkjet
inks which exhibit good jetting performance and good resulting image
durability are described in U.S. Publication No. 2004/0085419.

[0042]The polyurethane used in the invention has a weight average
molecular weight, Mw, of greater than 7,500. If Mw is less than 7,500,
then the inkjet ink composition may not provide adequate stain and
scratch resistance. A Mw of greater than 10,000 is typically preferred.
The maximum Mw of the polyurethane is not particularly limited, but is
generally dictated by the physical property requirements of the
composition and the method by which it will be applied, as discussed
below. If the ink composition is used as an inkjet ink for a thermal
printhead, then the maximum Mw of the polyurethane is suitably 30,000.
The acid number of the polyurethane is provided by acid groups that are,
in turn, provided by the at least one monomer comprising at least two
hydroxyl groups. The acid groups are preferably carboxylic acid groups,
but any type of acid groups can be used. The polyurethane latex binder
can have an acid number from 50 to 200 and desirably has an acid number
from 60 to 150 and typically from 70 to 90. The polyurethane used in the
invention can exhibit a Tg of from 20 to 180° C., typically from
40 to 120° C., and more suitably from 60 to 100° C.

[0043]Inks of the invention can optionally include up to 3% by weight of a
water soluble polyacrylate polymer. The water soluble polyacrylate
polymers can be either addition polymers or condensation polymers, both
of which are well known to those skilled in the art of polymer chemistry.
Specific examples include, but are not limited to: acrylic acid polymer;
methacrylic acid polymer; styrene-acrylic acid copolymer, styrene-acrylic
acid-acrylic acid alkyl ester copolymer, styrene-maleic acid copolymer,
styrene-maleic acid-acrylic acid alkyl ester copolymer,
styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid
alkyl ester copolymer, styrene-maleic acid hemi ester copolymer, vinyl
naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid
copolymer and so forth. Especially preferred water soluble polyacrylate
polymers include benzylmethacrylate-acrylic acid copolymers and
styrene-maleic acid hemi ester copolymers. These polymers are rendered
water soluble by the presence of the acid group originating in the
acrylic acid, maleic acid or methacrylic acid moiety of the polymer. For
polymers including acid groups, the extent of polymer charge
stabilization is quantified as the polymer acid number (AN). A calculated
polymer acid number is defined as the number of moles of acid monomer per
gram of polymer times 56 (which is the molecular weight of potassium
hydroxide). A measured acid number is the number of moles of acid found
per gram of polymer times 56, when titrating with potassium hydroxide in
water. The water soluble polyacrylate polymer suitably exhibits an acid
number from 100 to 400 and usually from 120 to 300 and a weight average
molecular weight Mw from 5,000 to 20,000 and more typically from 6,000 to
16,000.

[0044]The inks useful in the invention are subject to the proviso that the
weight ratio of dispersed pigment to the sum of water soluble
polyacrylate polymer (if any) and polyurethane latex binder is from 3:1
to 1:2. More usefully, the weight ratio of dispersed pigment to the sum
of water soluble polyacrylate polymer and polyurethane latex binder is
from 2:1 to 1:2. Most typically, the weight ratio of dispersed pigment to
the sum of water soluble polyacrylate polymer and polyurethane latex
binder is from 2:1 to 1:1. Lower quantities of polymer can cause poor
jetting or poor film formation while higher quantities of polymer can
cause poor jetting, clogging of ejectors or printer maintenance stations
and ink coalescence on many printing media.

[0045]Additional polymers can be present in the inkjet inks of the
invention. The polymers can act as binders or jetting-aids. These
polymers can be classified as water-soluble polymers, water-reducible
polymers or water-dispersible polymeric particles.

[0046]By the term "water-soluble" is meant that the polymer is dissolved
in water such that scattering is not observed when a dilute solution of
the polymer is analyzed using dynamic light scattering or any other
technique well known in the art of particle analysis.

[0047]By the term "water-reducible" is meant that the polymer can be
diluted with water to form reasonably stable dispersions of polymer
aggregates swollen by solvent and water, as described in "Organic
Coatings: Science and Technology" (2nd Edition by Wicks, Jones and Papas,
published by Wiley-Interscience, 1999). Such polymers have hydrophilic
groups in some monomers, but are not water soluble until neutralized by
base.

[0048]By the term "water-dispersible" is meant that the polymer exists in
the form of discrete particles in water, the particles being dispersed or
suspended and often stabilized against flocculation and settling by the
use of dispersing agents. In contrast to a water-soluble polymer, a
dilute solution of a water-dispersible polymer exhibits scattering when
analyzed using dynamic light scattering or any other technique well known
in the art of particle analysis.

[0050]The water-dispersible polymer particles are generally classified as
either addition polymers or condensation polymers, both of which are well
known to those skilled in the art of polymer chemistry. Examples of
water-dispersible polymer particle classes include acrylics, styrenics,
polyethylenes, polypropylenes, polyesters, polyamides, polyurethanes,
polyureas, polyethers, polycarbonates, polyacid anhydrides, and
copolymers consisting of combinations thereof. Such polymer particles can
be ionomeric; film forming, non-film-forming, fusible, or heavily
cross-linked and can have a wide range of molecular weights and glass
transition temperatures.

[0051]Examples of water dispersible polymeric particles used in inkjet
inks are styrene-acrylic copolymers sold under the trade names
Joncryl® (S. C. Johnson Co.), Ucar® (Dow Chemical Co.),
Jonrez® (MeadWestvaco Corp.), and Vancryl® (Air Products and
Chemicals, Inc.); sulfonated polyesters sold under the trade name Eastman
AQ® (Eastman Chemical Co.); polyethylene or polypropylene resin
emulsions and polyurethanes (such as the Witcobonds® from Witco
Corp.). Core-shell polymer particles have also been employed inkjet inks
for water-fastness and rub-resistance improvements (U.S. Pat. Nos.
5,814,685; 5,912,280; 6,057,384; 6,271,285; and 6,858,301). Additional
examples of water dispersible polymer particles include the thermoplastic
resin particles as disclosed in U.S. Pat. Nos. 6,147,139 and 6,508,548.
The polymer particles can be a mixture of high and low glass transition
temperature polymers such as those disclosed in U.S. Pat. No. 6,498,202.
Additionally, core-shell polymer particles as described in U.S. Pat. Nos.
5,814,685; 5,912,280; 6,057,384; 6,271,285; and 6,858,301 can be
employed. It is also possible to include in the ink, in addition to the
durability enhancing polymer particles, heavily cross-linked polymer
particles.

[0052]Ink compositions useful in the invention include one or more
water-soluble humectants, also called co-solvents, in order to provide
useful properties to the inkjet ink. Typical useful properties include
but are not limited to: preventing the ink composition from drying out or
crusting in the nozzles of the printhead, aiding solubility of the
components in the ink composition, aiding firing properties of the ink
from an ejector, facilitating penetration of the ink composition into the
image-recording element after printing, aiding gloss, suppressing
intercolor bleed, suppressing coalescence, and suppressing mechanical
artifacts such as paper cockle and curl during and after printing. Any
water-soluble humectant known in the ink-jet art can be employed. By
water-soluble is meant that a mixture of the employed humectant(s) and
water is homogeneous. While an individual humectant can be employed,
useful inkjet inks can employ mixtures of two, three or more humectants,
each of which imparts a useful property to the inkjet ink. Representative
examples of humectants and co-solvents used in aqueous-based ink
compositions include (1) alcohols, such as methyl alcohol, ethyl alcohol,
n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol,
t-butyl alcohol, iso-butyl alcohol, firfuryl alcohol, and
tetrahydrofurfuryl alcohol; (2) polyhydric alcohols, such as ethylene
glycol, diethylene glycol, triethylene glycol, tetraethylene glycol,
propylene glycol, dipropyleneglycol, the polyethylene glycols, the
polypropylene glycols, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol,
1,3-butanediol, 1,4-butanediol, 1,2,4-butanetriol,
3-methyl-1,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol,
1,6-hexanediol, 2-methyl-2,4-pentanediol, 1,7-hepanediol,
2-ethyl-1,3-hexane diol, 2,2,4-trimethyl-1,3-pentane diol, 1,8-octane
diol, glycerol, 1,2,6-hexanetriol, 2-ethyl-2-hydroxymethyl-propanediol,
2-methyl-2-hydroxymethyl-propanediol, saccharides and sugar alcohols and
thioglycol; (3) polyoxygenated polyols and their derivatives such as
diglycerol, polyglycerols, and the alkylated and acetylated derivatives
of glyceryths, pentaerythritol ethoxides, and pentaerythritol propoxides;
(4) nitrogen-containing compounds such as urea, 2-pyrrolidone,
N-methyl-2-pyrrolidone, imidazolidinone, N-hydroxyethyl acetamide,
N-hydroxyethyl 2-pyrrolidinone, 1-(hydroxyethyl)-1,3-imidazolidinone and
1,3-dimethyl-2-imidazolidinone; and (5) sulfur-containing compounds such
as 2,2'-thiodiethanol, dimethyl sulfoxide and tetramethylene sulfone. Of
these, glycerol and the polyhydric alcohol derivatives thereof are
preferred and glycerol is especially preferred. The polyhydric alcohol
derivatives of glycerol include the glycerol ethoxides, glycerol
propoxides and glyceryths. The humectants can be employed alone or in
combination with one or more additional listed humectants. When glycerol
and the polyhydric alcohol derivatives thereof are employed, they can be
employed at from 1 to 20% by weight, typically from 2 to 15% by weight
and suitably from 3 to 10% by weight. While any quantity of water soluble
humectants singly or in combination can be employed, the total quantity
of water soluble humectant is typically from 3 to 45 percent by weight
and typically from 8 to 35 percent by weight. Typical aqueous-based ink
compositions useful in the invention can contain, for example, the
following components based on the total weight of the ink: water 50-95%,
and humectant(s) 3-45%.

[0053]The pH of the aqueous ink compositions of the invention can be
adjusted by the addition of organic or inorganic acids or bases. Useful
inks can usually have a pH of from 2 to 10, depending upon the type of
dye or pigment being used and depending on the charge characteristics of
the other ink components employed. Anionic charge stabilized
anti-abrasion polymers are employed in inks having a pH of above 6, with
suitable pH ranges of from 7 to 11 and a typical pH range of from 7.5 to
10. Typical inorganic acids include nitric, hydrochloric, phosphoric and
sulfuric acids. Typical organic acids include methanesulfonic, acetic,
formic and lactic acids. Typical inorganic bases include alkali metal
hydroxides and carbonates including but not limited to sodium hydroxide
and potassium hydroxide.

[0054]Surprisingly, the well-known amine bases often used as pH adjustment
agents and buffers can cause marked degradation in the fireability and
stability of the ink of the invention. Accordingly, the ink of the
invention is free of an ejection disabling quantity of a water soluble
amine. By free of a water soluble amine, is meant that the ink does not
include a firing compromising quantity of a water soluble amine. A firing
compromising quantity of water soluble amine is that quantity of water
soluble amine that causes a decrease in firing velocity of more than 15%
or an increase in ink TTrns of greater that 95% relative to the firing
characteristics of the same ink that does not contain the water soluble
amine. Inks can be evaluated for jetting performance in a thermal inkjet
print head as follows: Ink is supplied to a thermal print head with 6 pL
nozzles. The jetting velocity and the transit time for each drop to
travel 0.3 mm from the nozzle plate is measured for 250 drops at each of
a set of varying firing frequencies from 280 to 27,720 Hz at an operating
voltage of 12% above the threshold voltage required for firing the inks.
The 0.3 mm distance is typical of the distance between the ejector and
the receiving paper surface in a typical inkjet printer. The average
velocity and the root mean square variation (rms) of the transit times
(TTrms) are calculated for 3 sets of firings of 10 different nozzles
fired at identical conditions (30 firing sets total). In a practical
sense, this means that the ink should comprise less than 0.05% by weight,
preferably less than 0.03% by weight and more preferably less than 0.01%
by weight of the water soluble amine, or is free of water-soluble amines.
Typical water soluble amines include but are not limited to ammonia,
ethanolamine, triethanolamine, dimethylethanolamine, N-methylmorpholine
and so forth. Distinct water soluble amines can cause different degrees
of ink firing degradation.

[0055]Inkjet ink compositions can also contain non-colored particles such
as inorganic particles or polymeric particles. The use of such
particulate addenda has increased over the past several years, especially
in inkjet ink compositions intended for photographic-quality imaging. For
example, U.S. Pat. No. 5,925,178 describes the use of inorganic particles
in pigment-based inks in order to improve optical density and rub
resistance of the pigment particles on the image-recording element. In
another example, U.S. Pat. No. 6,508,548 describes the use of a
water-dispersible polymer in dye-based inks in order to improve light and
ozone resistance of the printed images. For use of such particles to
improve gloss differential, light and/or ozone resistance, waterfastness,
rub resistance and various other properties of a printed image; see for
example, U.S. Pat. No. 6,598,967. Colorless ink compositions that contain
non-colored particles and no colorant can also be used. Colorless ink
compositions are often used in the art as "fixers" or insolubilizing
fluids that are printed under, over, or with colored ink compositions in
order to reduce bleed between colors and waterfastness on plain paper;
see for example, U.S. Pat. No. 5,866,638 or U.S. Pat. No. 6,450,632.
Colorless inks are also used to provide an overcoat to a printed image,
usually in order to improve scratch resistance and waterfastness; see for
example, U.S. Publication No. 2003/0009547 A1 or European Patent No.
1,022,151 A1. Colorless inks are also used to reduce gloss differential
in a printed image; see for example: U.S. Pat. No. 6,604,819; and U.S.
Publication Numbers 2003/0085974; 2003/0193553; or 2003/0189626.

[0057]Surfactants can be added to adjust the surface tension of the ink to
an appropriate level. The surfactants can be anionic, cationic,
amphoteric or nonionic and used at levels of 0.01 to 5% of the ink
composition. Examples of suitable nonionic surfactants include, linear or
secondary alcohol ethoxylates (such as the Tergitol® 15-S and
Tergitol® TMN series available from Union Carbide and the Brij®
series from Uniquema), ethoxylated alkyl phenols (such as the Triton®
series from Union Carbide), fluoro surfactants (such as the Zonyls®
from DuPont; and the Fluorads® from 3M), fatty acid ethoxylates,
fatty amide ethoxylates, ethoxylated and propoxylated block copolymers
(such as the Pluronic® and Tetronic® series from BASF,
ethoxylated and propoxylated silicone based surfactants (such as the
Silwet® series from CK Witco), alkyl polyglycosides (such as the
Glucopons® from Cognis) and acetylenic polyethylene oxide surfactants
(such as the Surfynols from Air Products). Additionally any
conformationally asymmetric water-soluble polyoxygenated hydrocarbons
enabling surface tension reduction can be employed as a surfactant.
Dynamic surface tension reducing agents as known in the art can also be
employed. Examples include the known lower mono-alkyl ethers derived from
the polyhydric alcohols; glycol specific examples include but are not
limited to ethylene glycol monomethyl ether, ethylene glycol monobutyl
ether, ethylene glycol monoethyl ether acetate, diethylene glycol
monomethyl ether, diethylene glycol monobutyl ether, polyethylene
monobutyl ether, propylene glycol monopropyl ether and diethylene glycol
monobutyl ether acetate, among others all as supplied as the
Dowanol®, Cellusolve®, and Carbitol® series from Dow
Chemical. Additional examples include the surface active lower alcohols;
specific examples include but are not limited to: 1,2-butanediol,
1,2-pentanediol, 1,2-hexanediol, 1-phenyl-1,2-ethanediol,
1,2-heptanediol, 1,2-octanediol, 1,3,6-hexanediol, 1,6-hexanediol and
1,3-hexanediol.

[0060]The exact choice of ink components will depend upon the specific
application and performance requirements of the printhead from which they
are jetted. Thermal and piezoelectric printheads which can function
either in drop-on-demand ink ejection mode or continuous ink ejection
mode each require ink compositions with a different set of physical
properties in order to achieve reliable and accurate jetting of the ink,
as is well known in the art of inkjet printing. Acceptable viscosities
are no greater than 20 cP, and preferably in the range of about 1.0 to
6.0 cP and more preferably in the range of 1.5 to 4 cP. Acceptable static
surface tensions are no greater than 60 dynes/cm, and preferably in the
range of 28 dynes/cm to 45 dynes/cm.

[0061]The inks are preferentially applied to a paper by thermal or piezo
ejection. Preferentially, an inkjet printhead capable of achieving firing
frequencies of at least 12 kHz with a near nozzle velocity of at least 10
meters/second is employed. Any of the known printhead designs in the art
of inkjet printing can be used provided they can achieve these high speed
firing frequencies. Preferably, the IJ printer is equipped with a thermal
inkjet printhead. Particularly preferred printhead designs are disclosed
in U.S. Publication Number 2006/0103691 and unpublished copending
application U.S. patent application Ser. No. 11/609,365; filed 12 Dec.
2006.

[0062]The inks of the invention can be used alone or they can be used in
combination. When used alone, the ink can be employed in a monochrome
printer. When used in combination, the inks can be of similar color as in
a monochrome printer or of distinct color as in a full color printer.
When used in combination, two inks of similar color but distinct
composition, such as a light ink and a dark ink can be used to form a
finely graduated or continuous photo-tone image. Alternatively, distinct
colored inks can be combined to form an inkjet ink set. When inks
according to the invention are used in combination, they are preferably
applied in an overlapping mode to a common area of the paper or in
non-overlapping mode to adjacent areas of the paper, all as known in the
inkjet ink application art. A color ink set preferably has at least cyan,
magenta, and yellow colored inks with optimal additions of black ink(s),
such as Photo-black inks and text black inks, clear inks to act as gloss
aids and protective overcoats and optional red, green, blue, brown,
orange, violet, photo-cyan and photo-magenta inks, and so forth to aid in
pictorial reproduction, all as known in the inkjet art. A color ink set
can contain both distinct colored inks and similarly colored inks of
distinct composition. The inkjet ink set according to the invention can
comprise the inventive ink alone or in several inks of the inkjet ink
set.

[0063]The inkjet inks, inkjet ink-sets and image forming methods described
above can be usefully employed with any suitable inkjet image receiver
known in the art. This includes, but is not limited to both matte and
glossy forms of plain papers, cardstocks, cardboards, transparent or
opaque plastics and vinyls, treated papers, coated papers and multilayer
image receivers. The glossy receivers are especially preferred as imaging
media for use with the inventive inkjet inks, inkjet ink-sets, and inkjet
image forming methods.

[0064]The inkjet inks of the invention can be packaged in an art known
inkjet ink container suitable for supplying ink to an ink ejector. The
container can have one or more ink reservoirs each holding a distinct
inventive ink. In one embodiment, intended for desktop applications, the
reservoirs can individually hold up to about 20 ml of ink. In embodiments
intended for commercial applications, the reservoirs can individually
hold up to about 5 liters of ink.

EXAMPLES

[0065]Acrylic Polymeric AP-1: A copolymer of benzylmethacrylate and
methacrylic acid having an acid number of about 135 as determined by
titration method, a weight average molecular weight of about 7,160 and
number average molecular weight of 4,320 as determined by the Size
Exclusion Chromatography. The polymer is neutralized with potassium
hydroxide to have a degree of neutralization of about 85%.

[0066]Acrylic Polymeric AP-2: SMA17352®, a styrene maleic anhydride
copolymer commercially available from SARTOMER COMPANY INC. and having an
acid number of about 270. The polymer is neutralized with potassium
hydroxide to have a degree of neutralization of about 85%.

[0067]Polyurethane PU-1; A 76 acid number polyurethane with a weight
average molecular weight of 13,300 made with isophorone diisocyanate and
a combination of poly(hexamethylene carbonate) diol and
2,2-bis(hydroxymethyl)propionic acid where 100% of the acid groups are
neutralized with potassium hydroxide.

[0069]A mixture of polymeric beads (milling media), CI Pigment Blue 15:3
(Sun Chemical Corp.), and an aqueous solution of potassium
oleylmethyltaurate was prepared and diluted with distilled water. The
mixture was milled for 24 hours and the milling media was separated from
the pigment dispersion. The resulting pigment dispersion was then
filtered through a one-micrometer binder-free glass fiber filter (Pall
Corp.) to obtain the final pigment dispersion having approximately 10% of
pigment and 2.5% dispersant. The resulting dispersion of cyan pigment
particles was measured for particle size using a Nanotrac® NAS 35
instrument from Microtrac Incorporated and had a median particle size
diameter of 0.05 microns.

Magenta Pigment Dispersion MD-1

[0070]A mixture of polymeric beads (milling media), CI Pigment Red 122
(Sun Chemical Corp.), and an aqueous solution of potassium
oleylmethyltaurate was prepared and diluted with distilled water. The
mixture was milled for 24 hours and the milling media was separated from
the pigment dispersion. The resulting pigment dispersion was then
filtered through a one-micrometer binder-free glass fiber filter (Pall
Corp.) to obtain the final pigment dispersion having approximately 10% of
pigment and 3% dispersant. The resulting dispersion of cyan pigment
particles was measured for particle size using a Nanotrac® NAS 35
instrument from Microtrac Incorporated and had a median particle size
diameter of 0.015 microns.

Carbon Black Pigment Dispersion CB-1

[0071]A mixture of polymeric beads (milling media), carbon black pigment
(Black Pearls® 880, Cabot Corporation), and an aqueous solution of
potassium oleylmethyltaurate was prepared and diluted with distilled
water. The mixture was milled for 24 hours and the milling media was
separated from the pigment dispersion. The resulting pigment dispersion
was then filtered through a one-micrometer binder-free glass fiber filter
(Pall Corp.) to obtain the final pigment dispersion having approximately
10% of pigment and 3% dispersant. The resulting dispersion of carbon
black pigment particles was measured for particle size using a
Nanotrac® NAS 35 instrument from Microtrac Incorporated and had a
median particle size diameter of 0.074 microns.

Preparation of Inks

[0072]A series of cyan pigment inks were prepared according to the
formulations provided in Table 1 using cyan pigment dispersion CD-1 as
the source of pigment particles.

[0074]A series of black pigment inks were prepared according to the
formulations provided in tables 3, 4 and 5 using pigment dispersion CB-1,
magenta pigment dispersion MD-1 and cyan pigment dispersion CD-1 as the
source of pigment particles.

[0075]Evaluation of Jetting Performance in a Thermal Inkjet Print Head.

[0076]Inks were evaluated for jetting performance in a thermal inkjet
print head after six to eight weeks keeping under normal storage
conditions of room temperature (approximately 20° C.). In
addition, selected inks were incubated at elevated temperatures according
to the following procedure. A sample of ink was placed in a high-density
polyethylene bottle with a sealed cap and placed in an oven at 60°
C. for 6-8 weeks. The inks were removed from the oven and allowed to cool
to room temperature. The jetting properties were then measured as
described below.

[0077]Each ink was supplied to a thermal print head with 6 pL nozzles. The
jetting velocity and the transit time for each drop to travel 0.3 mm from
the nozzle plate was measured for 250 drops at each of a set of varying
firing frequencies from 280 to 27,720 Hz at an operating voltage of 12%
above the threshold voltage required for firing the inks. The 0.3 mm
distance is typical of the distance between the ejector and the receiving
paper surface in a typical inkjet printer. The average velocity and the
root mean square variation (rms) of the transit times (TTrms) were
calculated for 3 sets of firings of 10 different nozzles fired at
identical conditions (30 firing sets total)

[0078]The data presented in Tables 6, 7 and 8 illustrate that the
inventive inks exhibit improved ink average velocities and reduced noise,
as measured by TTrms, under both mild and harsh condition keeping
conditions.

[0079]Inks generally like those in the above ink sets were prepared with
pigment dispersions that had been ground to distinct particle sizes to
form inks 101 through 118. These inks were individually printed onto
Kodak Glossy Media and the 20 deg gloss measured using a Glossometer.
Higher Gloss readings correspond to a more reflective image reminiscent
of traditional photographic images. These results are reported in Table 9
below.

[0087]When these six inks were evaluated for firing as described above,
the three inventive inks exhibited an average velocity (TTrms) of 15.3
m/s (0.2), 14.7 m/s (0.2) and 12.2 m/s (0.2) respectively while the first
two comparative inks would not fire in a stable enough fashion to allow
determination of an average velocity and showed very high noise (25.0)
and (10.4) respectively and the third comparative ink showed a large
decrease in velocity with a doubling of the noise, thus demonstrating the
detrimental effect of the presence of a water soluble amine on the
operation of the invention.

[0088]The invention has been described in detail with particular reference
to certain preferred embodiments thereof, but it will be understood that
variations and modifications can be effected within the spirit and scope
of the invention. The entire content of the patents and publications
referred to in this document are incorporated herein by reference.